1. Field of the Invention
The present invention relates to container articles formed of stratified or layered plastic material and to a method of making same.
2. Description of the Prior Art
The common tin can container, while possessing several advantages, including relatively low cost, nonbreakability, high heat resistance, etc., has many disadvantages, such as contamination of the contents of the can in the event the integrity of the can or varnish coating on the steel material is lost, difficulty in opening, etc. However, the provision of a feasible substitute for the ordinary tin can has proven elusive to date. While efforts have been made to provide a comparable plastic container, the unavailability of a plastic substance having all the properties necessary for the material for such a container has prevented realization of a satisfactory substitute.
Another problem is that of joinder of the parts of a plastic container. The use of adhesives is undesirable because of possible contamination of the contents of the container. Low cost plastic container materials, such as polyethylene, cannot be easily joined by readily available adhesives. Heat-seal bonds, formed by heated bars, and the like, have left much to be desired in terms of processing speed and the integrity of the bond and its strength.
The gist of the present invention is to employ, in the manufacture of container articles, a stratified material which advantageously combines the desirable properties of several different types of plastics. For example, the various layers of the stratified material may present a barrier to gas and/or moisture transmission or give strength, bulk, grease and scuff resistance, or heat resistance to the material.
Another feature of the present invention is to obviate the joinder problems heretofore encountered in the manufacture of plastic containers by providing a heat generating layer in the stratified material. This may typically be accomplished by dispersing in one of the layers a particulate material susceptible to heating by an alternating magnetic field through hysteresis losses. The advantages of the technique of the present invention includes, among others, concentration of the heat at or near the bonding interface, close control of bonding temperature, and ease of handling since no adhesive or other bonding accessories are required.
Since many of the susceptible particulate materials, hereinafter termed susceptors, possess undesirable colorations, the coloration caused by incorporation of the susceptor may be masked with an opaque layer, for example by a white layer, to hide the particle coloration.